Vacuum interrupter contacts having energy dissipation surfaces

ABSTRACT

A vacuum type circuit interrupter is provided having separable mating contacts. Multiple arc energy dissipating surfaces are attached to each contact. The arc energy dissipation surfaces are spaced from the contact to which they are attached, and at least a portion of the surfaces extend longitudinal of the vacuum interrupter. The arc is initiated at the primary contact surfaces, adjacent the central point of separable contact structure, and is moved to the arc dissipation surfaces which extend radially and/or axially from the contacts. The arc is rapidly moved to the energy dissipation surfaces and the primary contact surfaces are prevented from becoming eroded.

United States Patent [191 Hundstad VACUUM INTERRUPTER CONTACTS HAVING ENERGY DISSIPATION SURF ACES [75] Inventor: Richard L. Hundstad, Pittsburgh,

[73] Assignee: Westinghouse Electric Corporation,

Pittsburgh, Pa.

[22] Filed: June 20, 1972 [21] Appl. No.: 264,700

[52] [1.8. Cl..... 200/l44 13, 200/166 B, 200/166 BH [51] Int. Cl. H0lh 33/66 [58] Field of Search 200/144 B, 166 B, 166 BH [56] References Cited UNITED STATES PATENTS Hundstad 200/144 B v 1 June 4, 1974 FOREIGN PATENTS OR APPLICATIONS 213,125 12/1968 U.S.S.R. 200/144 B Primary Examiner-R0bert S. Macon Attorney, Agent, 0r Firm-H. G. Massung 5 7] ABSTRACT pation surfaces and the primary contact surfaces are prevented from becoming eroded.

5 Claims, 15 Drawing Figures PATENTEDJM 4 1914 88141880 SHEEI 2 ur 3 1' I VACUUM INTERRUPTER CONTACTS HAVING ENERGY DISSIPATION SURFACES BACKGROUND OF THE INVENTION The present invention concerns a concept for separavble contacts or electrodes for a vacuum type circuit interrupter. More specifically the present invention is concerned with a means of utilizing energy dissipation surfaces to aid in arc control during circuit interruption and to preserve the integrity of the primary contact surfaces.

A vacuum type circuit interrupter comprises a pair of movable contacts disposed within a highly evacuated insulating envelope. These contacts are movable between a closed position in which they are in electrical contact and an open position in which the contacts are separated, and an arcing gap is established therebetween; During circuit interruption, the contacts are separated and an arc is established across the arcing gap. On an alternating current circuit the arc is normally maintained until approximately the first current zero, of the alternating current wave, at which time the arc is extinguished. If most of the particles and vapors generated by the are are quickly removed the vacuum regains its high dielectric strength and the arc is kept from reigniting, thereby completing circuit interruption.

The primary contact surfaces in conventional vacuum type circuit interrupters are subject to very intense heat during arcing. The contact surfaces must support the arc from its initiation at the time of electrode separation until its extinction at approximately zero current. The are energy causes melting, erosion, and gen-. eral deterioration of the contact surfaces. Prior art contact constructions partially circumvent this problem by providing primary surfaces for conducting the current during normal steady state operation and additional surfaces surrounding the primary surfaces for are energy dissipation during circuit interruption. According to the apparent theory of operation the arc is driven from the primary contact surfaces following separation and then rotates on the energy dissipation surfaces until extinction takes place. Spiral slots in the energy dissipation surfaces cause the arc to spiral radially outward under the influence of self-induced magnetic forces. The are is then rotated around the contact surface under the influence of the magnetic forces. Experimental tests of vacuum switches embodying this construction have shown that the design is only partially successful. It appears that the spiral slots although quite effective in rotating the arc do not confine the intense heat and resulting deterioration to the energy dissipation surfaces. General deterioration of adjacent contact surfaces result.

Measurements indicate that the interrupting capability of the contacts tend to increase with the size and surface area available for arcing. Contact area however is effective in the arc interruption process only if it is in intimate contact with the arc plasma. Increased contact area is known to be beneficial in arc interruption even though the extended contact area is somewhat remote from the contact surfaces. This beneficial effect is thought to partially result from the lower mean temperature of the electrode due to the lower energy density in the contact and electrode. It is also desirable that vacuum interrupter contacts have a relatively open construction to permit rapid expansion of the vapors and gases formed during arc interruption, from the inner electrode space, to permit the vacuum to quickly recover its high dielectric strength.

In prior art contacts the energy dissipation surfaces are separated a greater distance than the primary contacts surface. This makes theenergy dissipation surfaces less effective in anchoring the are because of the arcs tendency tomove to the higher electric field region between the contact surfaces. Closer spacing of the energy dissipation surfaces provides greater and more effective use of the magnetic force to move the are away from the contact surfaces. Due to the power dissipated in a large current are, it is advantageous to keep the arc length short and thereby limit the energy released during an interruption.

It has also been a problem with prior art contacts that the arc can interact with the main arc shield. It has been found experimentally that current interruption limits are reached when the arc interacts with the main shield. In most cases a hole is melted in the arc shield and the interrupter fails. It is therefore desirable that the are be controlled so that during circuit interruption it does not interact with the shield.

SUMMARY OF THE INVENTION According to the present invention a contact construction for a vacuum type circuit interrupter is provided having primary contact surfaces and secondary or are energy dissipation surfaces. The arc is initially established at the primary contact surfaces and then is moved to the arc dissipation surfaces and are extinction occurs at the latter secondary surfaces.

In one embodiment of the invention are rails extend radially outward from the primary contact surfaces. Arc energy dissipation surfaces are attached to the ends of the arc rails and run parallel to longitudinal axis of the vacuum interrupter. The are dissipation surfaces lie in a generally circular configuration. The energy dissipation surfaces of the first contact are interlaced with the energy dissipation surfaces of the second mating contact. During circuit interruption the are forms between the primary contact surfaces, and then, under the influence of the self-induced magnetic forces, is

moved to the arc dissipation surfaces. As the arc is moved from the primary contact surfaces to the are energy dissipation surfaces the direction of the arc is changed from axial to an azimuthal or circumferential direction. Arc extinction then occurs on the secondary contact surfaces.

In another embodiment of the invention the arc dissipation surfaces are attached directly to the primary contact surfaces and extend perpendicular thereto. The are dissipation surfaces are attached in a generally circular configuration and extend parallel to the longitudinal axis of the vacuum interrupter. The-arc dissipation surfacesextend in a radial and circumferential direction on the disc-shaped primary contact surfaces. The are energy dissipation surfaces of the mating contacts are interlaced. The spacing between the arcing surfaces varies being a minimum at the innermost radial position and a maximum near the outer periphery of the discshaped primary contact surface. This causes a higher electric field region to exist in the inner electrode space, to more effectively contain the are. If an arc does tend to bow out from the arcing surfaces towards the main shield the arc will be forced to bow in a some 3 what circumferential direction. This will help position the are so that there is less chance that it will interact with the main arcing shield.

In another embodiment of the invention the arc energy dissipation surfaces extend radially outward from the primary contact surface, and are angled away from the mating contact. In this embodiment both contacts are of a similar configuration and the spokes of each contact are in angular alignment. The outer portions of the arc energy dissipation surfaces are separated further than the inner portions which are attached to the primary contact surfaces. In this configuration the spokes are purposely made small in cross sectional area adjacent to the primary contact so as to concentrate the self-induced magnetic field as well as the arc columns and thereby effectively provide the necessary magnetic forces to move the arc radially outward and away from the primary contact surfaces. In a variation of this embodiment the mating contacts can be rotated to new angularpositions with respect to each other and arc rails can be angled towards the mating contact. Thus the end of the arc rails will be partially interlaced. The are formed during circuit interruption will move along the arc rails and change from a radial direction to an azimuthal direction. Also the ends of the arc rails can be extended parallel to the longitudinal axis of the vacuum interrupter toward the mating contact to further enhance the interlacing.

In other embodiment of the invention the arcing surfaces or spokes extend radially from the primary contact surfaces and then bend 90 so that they run parallel to the longitudinal axis of the vaccum interrupter. The mating contacts are not identical in shape. The portions of the arcing surfaces which run parallel to'the longitudinal axis extend in the same direction for both contacts. That is the free ends of all of the arcing surfaces of both of the contacts point in the same direction. In one variation the spokes of a first contact extend radially outward further than the spokes of its mating second contact and the mating second contact is located within the confines of the first contacts spokes. The spokes of both contacts are in angular alignment so that an arc formed during circuit interruption is moved from the axial direction to the radial direction, where it terminates on the arc dissipation surfaces. In another variation of this same embodiment the spokes of each contact extend radially outward to the same radial position and one contact is angularly rotated to a position where the spokes are in an interlacing configuration. An arc formed during circuit interruption will be moved from the axial direction to the azimuthal direction with this configuration. The spokes which extend from the contact surfaces are made small in cross sectional area adjacent to the primary contact buttons so as to concentrate the self-induced magnetic field as well as the arc columns and thereby effectively provide the necessary magnetic forces to move the arc outward and away from the primary contact surfaces.

BRIEF DESCRIPTION OF THE DRAWINGS Other advantages of the invention will be apparent from the following detailed description taken in conjunction with the accompanying drawings, in which:

FIG. 1 is a sectional view of a vacuum circuit interrupter comprising a contactstructure of one embodiment of the invention;

FIG. 2 is a top view of the contact structure shown in FIG. 1;

FIG. 3 is a side view partially in section of the contact structure shown in FIG. 2 along the line IIIIII;

FIG. 4 is a side view of a contact structure illustrating another embodiment of the invention;

FIG. 5 is a view of the contact structure shown in FIG. 4 along the line V-V;

FIG. 6 is a side view of a contact structure illustrating another embodiment of the invention;

FIG. 7 is a top view of the contact structure illustrated in FIG. 6;

FIG. 8 is a side view of a contact structure similar to that shown in FIG. 6 but with the contacts rotated relative to one another and with the spokes angled toward the mating contact;

FIG. 9 is a top view of the contact structure shown in FIG. 8;

FIG. 10 is a contact structure similar to that shown in FIG. 8 with the addition of arcing surfaces running parallel to the longitudinal axis of the vacuum interrupter;

FIG. 11 is a top view of the contact structure shown in FIG. 10;

FIG. 12 is a top view of a contact structure illustrating another embodiment of the present invention;

FIG. 13 is a side view of the contact structure shown in FIG. 12;

FIG. 14 is a top view ofa contact structure similar to that shown in FIG. 12 but with the contacts rotated relative to each other and with equal radial spacing of the arcing surfaces; and

FIG. 15 is a side view of the contact structure shown in FIG. 14.

DESCRIPTION OF THE PREFERRED EMBODIMENT Referring now to the drawings and FIG. 1 in particular thereis shown a vacuum type circuit interrupter 16. The vacuum circuit interrupter 16 comprises a highly evacuated tubular envelope 18 formed from glass or suitable ceramic material and a pair of metallic end caps 20 and 22 closing off the ends of the insulating envelope l8. Suitable seals 24 are provided between the end caps 20 and 22 and the insulating envelope 18 to render the inside of the insulating envelope l8 vacuum tight. The pressure within the envelope 18 under normal operating conditions is lower than 10" torr to ensure that the mean free path for electrons will be longer than the potential breakdown path within the envelope 18. Located within the insulating envelope 18 are a pair of relatively movable electrodes or contacts 26 and 28, as shown in FIG. 1 in the closed circuit position. When the contacts 26 and 28 are separated there is formed an arcing gap therebetween. The upper contact 26 is a stationary contact secured to a conducting rod 32 by a suitable means such as welding or brazing. The conducting rod 32 is rigidly joined to the stationary end cap 20 by a suitable means such as welding or brazing. The lower contact 28 is a movable contact and is joined to a conductive operating rod 34 by suitablmeans such as welding or brazing. The operating rod 34 is suitably mounted for movement along the longitudinal axis of the insulating envelope 18. The operating rod 34 projects through an opening 36 in the bellows end cap 22 as shown in FIG. 1. A metal bellows 38 is secured in sealing relationship at its respective opposite ends to the operating rod 34 and to the bellows end cap 22. The flexible metallic bellows 38 provides a seal about the operating rod 34 to allow for movement of the operating rod 34 without impairing the vacuum within the envelope l8.

Coupled to the lower end of the operating rod 34 is a suitable actuating means (not shown) for driving the movable contact 28 upward into engagement with the stationary contact 26 so as to close the interrupter 16. The actuating means is also capable of returning the movable contact 28 to its open circuit position during circuit inter'ruption. The circuit opening operation will entail a typical gap length when the contacts are fully separated of approximately one-half inch.

When the contacts 26 and 28 are separated during circuit interruption an arc is formed in the arcing gap between electrodes 26 and 28. The are which is formed between the contacts 26 and 28 vaporizes some of the contact material. These vapors and particles are dispersed from the arcing gap toward the insulating envelope 18. The internal insulating surfaces of the insulating-envelope 18 are protected from'the condensation of the are generated metallic vaporsand particles by means of a tubular metallic shield 40 which is suitably supported on the insulating envelope 18 and preferably electrically isolated from both end caps and 22. This shield 40 acts to intercept and to condense arc generated metallic vapors and particles before they can reach the insulating envelope 18. To further reduce the chances for vapors or particles reaching the insulating envelope 18, by bypassing the shield 40, a pair of end shields 42 and 44 are provided on opposite ends of the main central shield 40. A cup-shaped shield 43 is attached to the movable operating rod 34 and surrounds the flexible metallic bellows 38 to thus prevent the bellows 38 from being bombarded by are generated metallic vapors or particles. The speed with which the vapors generated during arcing are removed determines the steady state operating condition during arcing and also the recovery capability of the unit. If the vapor is not quickly removed high voltage transients might cause the arc to reignite after it has been extinguished resulting in failure of the interrupter 16. The are interacting with the magnetic shield 40 and melting a hole therethrough is the cause of many of the failures noted in vacuum interrupters 16.

Because of the high power density impressed upon the contacts 26 and 28 during the arcing interval substantial erosion takes place and it is therefore desirable to move the established are away from the primary contact surfaces 50. Referring now to FIGS. 2 and 3 it can be seen that the contact structures shown comprise a portion 51 extending radially outward from the primary contact surfaces 50 and an are energy dissipation portion 52 attached to the ends of the radially extending portions 51. The are energy dissipation portions 52 run generally parallel to the support rod 32. The arcing surfaces 52 of contacts 26 and 28 are assembled in an interlacing configuration. When contacts 26 and 28 are separated during circuit interruption an arc is formed between the primary contact surfaces 50. This are moves out on the arc rails 51 to the arcing surfaces 52.

The are is contained between the surfaces 52 until it is extinguished at a current zero. Note that when the are moves from the primary contact surface 50 to the arcing surfaces 52 that the longitudinal axis of the are changes from an axial direction to an asymmetric or circumferential direction. Arc barriers 54 as shown in FIG. 1 are placed near the ends of the arc dissipation surfaces to prevent an arc, between the arc dissipation surfaces 52, from bowing out towards the ends 20 or 22 of the vacuum circuit interrupter 16. By confining arcing between the arc dissipation surfaces 52, integrity of the primary contact surfaces is maintained.

Referring to FIGS. 4 and 5 there is shown a contact structure illustrating a second embodiment of the invention. In this embodiment the arcing surfaces attach directly to the primary contact surfaces 61 and extend perpendicular to the contact surfaces 61. The stationary contact 62 and the movable contact 63 have a generally disc-shaped portion which forms the main contact surface 61. The are dissipation surfaces 60 extend parallel to the longitudinal axis of the vacuum interrupter 16. The arcing surfaces 60 attach to the primary contact surface 61 in a circumferential and radial configuration. If an are between the arcing surfaces 60 bows out away from the contacts 62 and 63 it will be forced in a somewhat circumferential direction. Note that the spacing between the arcing surfaces of the opposite contacts is not a constant. There is agreater spacing between the arcing surfaces at the outer perimeter of the main contact area 61. This tends to contain the are within the inner electrode space.

Referring to FIGS. 6, 7, 8, 9, l0 and 11 there are shown contact constructions illustrating another embodiment of this invention. These figures show contacts in which spokes or arcing surfaces extend radially outward from and at an angle to the main contact surface 71. Note that at point 72 where the arc dissipation surface is joined to the primary contact surface 71 the cross sectional area of the arc dissipation surface is made relatively small in cross sectional area. That is, the cross sectional area of the arc dissipation portion 70 is relatively less at point 72 than at points spaced radially outward from point 72. The area 72 is purposely made small in cross section adjacent to the primary contact surface 71 so as to concentrate the self-induced magnetic fields as well as the arc columns, and thereby effectively provide the necessary magnetic force to move the arc radially outward and away from the primary contact surfaces 71.

Referring now to FIGS. 6 and 7 there is'shown a contact construction in which the arc dissipation surfaces 70'angle away from the mating contact. That is as shown in FIG. 6 the are dissipation surface 70 of contact 68 extend radially from contact 68 and angle away from contact 69. Likewise, the arcing surfaces 70 of contact 69 extend radially from contact 69 and angle away from mating contact 68. The distance between the arc dissipation portion 70 becomes greater at the radially outer positions.

' Referring now to FIGS. 8 and 9 there is shown a contact construction in which the arc dissipation portions slant towards the mating contact. That is the arc dissipation portion 78 of contact 69 extends radially from contact 69 and slants toward contact 68 and the arc dissipation portion 70 of contact 68 extends radially from contact 68 and slants toward contact 69. Contact 68 is rotated angularly with respect to contact 69 so that the arc dissipation portions are in an interlacing arrangement. Note that the arcing gap formed between contacts 68 and 69 is greater than the spacing between the 'arc dissipation surfaces 70 of contacts 68 and 69 when they are in the open circuit position. An

are formed between contacts 68 and 69 will be moved by the magnetic forces to the arc dissipation portion 70. The direction of the arc will be changed from the axial direction in which it originates to an azimuthal direction.

Referring now to FIGS. 10 and 11 there is shown a contact construction which is similar to that shown in FIGS. 8 and 9 with theaddition of a portion 74 to the 'end of the arc dissipation portion 70. Portion 74 extends generally parallel to the longitudinal axis of the vacuum-interrupter 16. These additional portions 74 aid in arc control and dissipation of the are energy.

, Referring now to FIGS. l2, l3, l4 and there is shown another embodiment of this invention. Arc dissipation portions 83 or 84 extend from the primary contact surface 82 radially for a distance thenbend 90 so as to be parallel with the longitudinal axis of the vacuum type circuit interrupter 16. During circuit interruption the direction of movement of the arc undergoes a rotation of 90 and the arc travels in a direction parallel to the longitudinal axis of the vacuum interrupter 16. With this embodiment the length as well as the width of the vacuum interrupter can be utilized for are control. The arc is controlledso that there is less possibility that it will interact with the main shield 40. An arc barrier 54 is provided to prevent any are formed during circuit interruption from bowing out and contacting the end of the vacuum interrupter 16. The are dissipation surfaces 83 are generally L-shaped in configuration. The are dissipation portion 83 of contact 80 extends past the main contact surface 82 of contact 81. The are dissipation surfaces 84 of contact 81 and 83 of contact 80 extend towards the end of the vacuum interrupter 16 through which control rods 34 passes.

Referring now to FIGS. 12 and 13 there are shown a pair of contacts 80 and 81 on which the arcing surfaces 84 of contact8l are smaller and radially inside the'arcing surface 83 of contact 80. As shown in FIG. 12 the arcing surfaces 83 and 84 are in radial alignment. An are which is formed during circuit interruption between the primary contact surfaces 82'is moved outward and then rotated 90 to a radial direction. Note that the point, where the arcing surfaces 83 or 84 join the primary contact surfaces 82, is of restricted cross section to aid in arc movement.

Referring now to FIGS. 14 and 15 there is shown a contact configuration in which contact 80 is rotated around its longitudinal axis with respect to contact 81. The are dissipation surfaces 84 of contact 81 extend radially outward as far as the arc dissipation surfaces 83 of contact 80. The free ends of arc dissipation surfaces 83 and 84 point in the same direction. An are formed between the primary contact surfaces 82 during circuit interruption is moved radially outward and rotated 90 to an azimuthal orientation. During circuit interruption arcing will continue between arc dissipation surface 84 and are dissipation surface 83 until the arc is extinguished.

This invention has several advantages for example the arc is quickly moved from the main contact surfaces to secondary contact surfaces where the arc energy can be dissipated without a deteriorative effect on the main contact area. Another advantage of this invention is the open type construction which allows vapors and particles generated during arcing to be quickly dispersed and permits the vacuum dielectric strength to be quickly recovered.

Since numerous changes may be made in the above described apparatus and different embodiments of the invention may be made without departing from the spirit and scope thereof it is intended that all the matter contained in the foregoing description and shown in the accompanying drawings shall be interpreted as illustrative and not in a limiting sense.

I claim as my invention:

1. A vacuum type circuit'interrupter comprising a highly evacuated tubular insulating envelope, a first contact structure disposed within said tubular insulating envelope, a second contact structure disposed within said tubular insulating envelope, said first contact structure and said second contact structure being mating contacts, said second contact structure being movable between a first position in contact with said first contact structure and a second position in which said second contact structure is spaced from said first contact structure, each of said contact structures comprising a main contact portion having a planar circular cross sectional configuration, a first plurality of are energy dissipation means attached to said first contact structure and being fixed in relation to said first contact structure, a second plurality of are energy dissipation means attached to said planar circular main contact portion of said second contact structure and unitarily movable therewith, at least a portion of each of said are energy dissipation means extending in a direction parallel to the longitudinal axis of said vacuum interrupter, each of said are energy dissipation means fixed relative to the associated main contact structure to which it is attached and extending radially outward from said main contact portion, and each of said are energy dissipation means also extending axially toward the mating contact structure beyond said main contact portion to which it is attached.

2. A vacuum type circuit interrupter including in combination means defining an evacuated envelope, a pair of separable mating contacts disposed within the evacuated envelope, said contacts being separable to establish arcing, and both of the separable contacts including a central main contact portion and a plurality of circumferentially spaced radially outward and axially extending conducting are energy dissipation portions, said are energy dissipation portions emanating only radially outward and axially from said central main contact portion and being connected and fixed in relation to the separable mating contact to which it is attached, and each of said arc energy dissipation portions extending towards the mating contact past said main contact portion to which it is attached.

3. A combination as claimed in claim 2 including a rectangular shaped portion connected to the end of said are energy dissipation portion and extending in an axial direction parallel to the longitudinal axis of said vacuum interrupter, said rectangular portion of each contact extending past said central main contact portion of its mating contact.

4. The combination as claimed in claim 2 wherein the crosssectional area of the inner portion of said energy dissipation portion is less than the cross sectional area of the outer portion of said energy dissipation portion.

said mating contact. 

1. A vacuum type circuit interrupter comprising a highly evacuated tubular insulating envelope, a first contact structure disposed within said tubular insulating envelope, a second contact structure disposed within said tubular insulating envelope, said first contact structure and said second contact structure being mating contacts, said second contact structure being movable between a first position in contact with said first contact structure and a second position in which said second contact structure is spaced from said first contact structure, each of said contact structures comprising a main contact portion having a planar circular cross sectional configuration, a first plurality of arc energy dissipation means attached to said first contact structure and being fixed in relation to said first contact structure, a second plurality of arc energy dissipation means attached to said planar circular main contact portion of said second contact structure and unitarily movable therewith, at least a portion of each of said arc energy dissipation means extending in a direction parallel to the longitudinal axis of said vacuum interrupter, each of said arc energy dissipation means fixed relative to the associated main contact structure to which it is attached and extending radially outward from said main contact portion, and each of said arc energy dissipation means also extending axially toward the mating contact structure beyond said main contact portion to which it is attached.
 2. A vacuum type circuit interrupter including in combination means defining an evacuated envelope, a pair of separable mating contacts disposed within the evacuated envelope, said contacts being separable to establish arcing, and both of the separable contacts including a central main contact portion and a plurality of circumferentially spaced radially outward and axially extending conducting arc energy dissipation portions, said arc energy dissipation portions emanating only radially outward and axially from said central main contact portion and being connected and fixed in relation to the separable mating contact to which it is attached, and each of said arc energy dissipation portions extending towards the mating contact past said maIn contact portion to which it is attached.
 3. A combination as claimed in claim 2 including a rectangular shaped portion connected to the end of said arc energy dissipation portion and extending in an axial direction parallel to the longitudinal axis of said vacuum interrupter, said rectangular portion of each contact extending past said central main contact portion of its mating contact.
 4. The combination as claimed in claim 2 wherein the cross sectional area of the inner portion of said energy dissipation portion is less than the cross sectional area of the outer portion of said energy dissipation portion.
 5. The combination as claimed in claim 2 wherein said arc energy dissipation portions are slanted toward said mating contact. 